Membrane vents are used, for example, in the automotive and telecommunications industries to equalize pressure between the interior and exterior of otherwise sealed enclosures. In membrane vents, membranes generally comprise porous air-transmitting material that is preferably impermeable to liquids. Membrane vents are therefore able to equalize pressure, while minimizing contamination of enclosure interiors.
The effectiveness of a membrane vent at pressure equalization is dependant upon both the material composition of the membrane, and upon the membrane's surface area. In the prior art, a membrane is approximately flat and arranged perpendicular to a small bore in the enclosure wall so as to completely cover the bore. This provides for a membrane surface area equal to or only slightly larger than the cross section of the bore, limiting the rate of pressure equalization. During periods of moderate to high changes in interior or exterior pressure, such limited rates of pressure equalization proves detrimental.